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diff --git a/share/doc/gcc/Garbage-Collection.html b/share/doc/gcc/Garbage-Collection.html new file mode 100644 index 0000000..fb30411 --- /dev/null +++ b/share/doc/gcc/Garbage-Collection.html @@ -0,0 +1,166 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +Copyright (C) 1988-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". + +(a) The FSF's Front-Cover Text is: + +A GNU Manual + +(b) The FSF's Back-Cover Text is: + +You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Using the GNU Compiler Collection (GCC): Garbage Collection</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): Garbage Collection"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Garbage Collection"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Indices.html#Indices" rel="index" title="Indices"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Objective_002dC.html#Objective_002dC" rel="up" title="Objective-C"> +<link href="Constant-string-objects.html#Constant-string-objects" rel="next" title="Constant string objects"> +<link href="Method-signatures.html#Method-signatures" rel="previous" title="Method signatures"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en_US" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Garbage-Collection"></a> +<div class="header"> +<p> +Next: <a href="Constant-string-objects.html#Constant-string-objects" accesskey="n" rel="next">Constant string objects</a>, Previous: <a href="Type-encoding.html#Type-encoding" accesskey="p" rel="previous">Type encoding</a>, Up: <a href="Objective_002dC.html#Objective_002dC" accesskey="u" rel="up">Objective-C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Garbage-Collection-1"></a> +<h3 class="section">8.4 Garbage Collection</h3> + +<p>This section is specific for the GNU Objective-C runtime. If you are +using a different runtime, you can skip it. +</p> +<p>Support for garbage collection with the GNU runtime has been added by +using a powerful conservative garbage collector, known as the +Boehm-Demers-Weiser conservative garbage collector. +</p> +<p>To enable the support for it you have to configure the compiler using +an additional argument, <samp><span class="nolinebreak">--enable-objc-gc</span></samp><!-- /@w -->. This will +build the boehm-gc library, and build an additional runtime library +which has several enhancements to support the garbage collector. The +new library has a new name, <samp>libobjc_gc.a</samp> to not conflict with +the non-garbage-collected library. +</p> +<p>When the garbage collector is used, the objects are allocated using the +so-called typed memory allocation mechanism available in the +Boehm-Demers-Weiser collector. This mode requires precise information on +where pointers are located inside objects. This information is computed +once per class, immediately after the class has been initialized. +</p> +<p>There is a new runtime function <code>class_ivar_set_gcinvisible()</code> +which can be used to declare a so-called <em>weak pointer</em> +reference. Such a pointer is basically hidden for the garbage collector; +this can be useful in certain situations, especially when you want to +keep track of the allocated objects, yet allow them to be +collected. This kind of pointers can only be members of objects, you +cannot declare a global pointer as a weak reference. Every type which is +a pointer type can be declared a weak pointer, including <code>id</code>, +<code>Class</code> and <code>SEL</code>. +</p> +<p>Here is an example of how to use this feature. Suppose you want to +implement a class whose instances hold a weak pointer reference; the +following class does this: +</p> +<div class="smallexample"> +<pre class="smallexample"> +@interface WeakPointer : Object +{ + const void* weakPointer; +} + +- initWithPointer:(const void*)p; +- (const void*)weakPointer; +@end + + +@implementation WeakPointer + ++ (void)initialize +{ + if (self == objc_lookUpClass ("WeakPointer")) + class_ivar_set_gcinvisible (self, "weakPointer", YES); +} + +- initWithPointer:(const void*)p +{ + weakPointer = p; + return self; +} + +- (const void*)weakPointer +{ + return weakPointer; +} + +@end + +</pre></div> + +<p>Weak pointers are supported through a new type character specifier +represented by the ‘<samp>!</samp>’ character. The +<code>class_ivar_set_gcinvisible()</code> function adds or removes this +specifier to the string type description of the instance variable named +as argument. +</p> +<hr> +<div class="header"> +<p> +Next: <a href="Constant-string-objects.html#Constant-string-objects" accesskey="n" rel="next">Constant string objects</a>, Previous: <a href="Type-encoding.html#Type-encoding" accesskey="p" rel="previous">Type encoding</a>, Up: <a href="Objective_002dC.html#Objective_002dC" accesskey="u" rel="up">Objective-C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |